1. Field of the Invention:
The present invention relates to an improvement of the surface structure of a heat radiating plate processed prior to soldering of a semiconductor device, said heat radiating plate comprising aluminum or aluminum alloy for cooling the semiconductor device.
2. Description of the Prior Art:
FIG. 1 shows the conventional semiconductor device of this kind. In the figure, the reference numeral (1) designates a heat radiating plate made of aluminum or aluminum alloy having a recess (1a); (2a) designates a plating layer covering the entire surface of the heat radiating plate (1), said plating layer being provided to provide a good soldering; (3) designates a semiconductor device such as a diode device attached in the recess (1a) of the heat radiating plate (1); and (4) designates a solder for bonding the semiconductor device (3) to the plating layer (2a).
The conventional device is prepared as follows: a heat radiating plate (1) is fabricated using aluminum or aluminum alloy; a recess (1a) for receiving a semiconductor device is formed at a predetermined position; plating is applied to the heat radiating plate to coat the entire surface with a plating layer (2a); a semiconductor device (3) is placed at a predetermined position in the recess (1a) of the heat radiating plate (1); and the semiconductor device (3) is bonded on the plating layer (2a) by solidifying a molten solder; thus the fabrication is completed.
In the conventional device, heat produced by the actuation of the semiconductor device (3) is conducted through the solder (4) and the plating layer (2a) to the heat radiating plate (1) so that the heat is radiated from the surface of the plating layer (2a) so as to cool the semiconductor device (3).
The conventional device has a disadvantage in that the plating layer (2a) easily becomes loose because of a local battery effect produced between pin-holes in the plating layer (2a) and a metal substrate different from the material of the layer except for the soldered portion because the entire surface of the heat radiating plate (1) is plated. The partial peeling of the layer produces an air gap between the heat radiating plate (1) and the plating layer (2a) resulting in inferior radiating. When the plating layer (2a) completely peels off, short-circuiting may occur in another circuit resulting in an erroneous operation.